Oops, it doesn't look like 'popcake day' is a national day..

Other days

law

Law Day
blanket fort

Blanket Fort Day
first love

First Love Day
gum

Gum Day
get funky

Get Funky Day
my little pony

My Little Pony Day
reading

Reading Day
self appreciation

Self Appreciation Day
offer

Offer Day
fiancee

Fiancee Day